Unloading of grain from harvesters such as combines, is typically accomplished using an elongate unloading tube including a helical auger contained therein. The unloading tube has a discharge opening through which grain is propelled by rotation of the auger. During an unloading process of the combine, grain is moved from a grain tank of the harvester to another tank or receptacle, such as on a truck or wagon.
A well-known problem associated with unloading systems of combine harvesters is that grain remaining in the unloading tube at the end of the unloading process can continue to dribble out of the discharge opening as the unloading tube is swung to its transport position. In addition, grain has been observed to dribble out of the discharge opening with the unloading tube in the transport position, particularly as the harvester is moved over rough terrain, up hills, and the like.
A variety of doors referred to as dribble doors, spill saver doors, or grain saver doors have been utilized in attempts to reduce the dribble problem. Usually these doors are biased, typically by a spring, to a closed position in covering relation to at least a portion of the discharge opening. As the auger rotates, grain is moved through the unloading tube to the discharge opening exerting a force against the door. As the force of the discharging grain increases, the spring yields allowing the door to open and the grain to discharge.
An observed shortcoming of these doors is that the biasing forces urging the door to the closed position tend to interfere with the flow of grain, especially when smaller or irregular amounts of grain are present. The force exerted against the door by the smaller or irregular amounts of grain may only be sufficient to partially open the door or to open the door by varying amounts as the amount of grain varies. The resulting flow of grain discharged may be irregular and/or varied, as influenced by the quantity of grain present, making it susceptible to redirection by wind drift. Even a small amount of wind drift can be significant because the grain is often unloaded while the combine is moving and the receiving vehicle is being driven or towed in parallel with the combine over rough terrain or furrows making steering difficult. Often the operator of the receiving vehicle may attempt to position one side or the other of the receiving vehicle more beneath the spout such that, with wind drift, the stream of grain will be directed more to the center of the receiving vehicle. This is facilitated by a tighter, more cohesive flow of discharging grain.
A variety of doors have been utilized in attempts to address these shortcomings. Reference in this regard, Reimer et al. U.S. Pat. No. 6,691,861 issued to Deere & Company, which discloses a dribble door pivotally mounted to a bottom periphery of an unloading tube, for preventing dribble when in a raised position, and which has a spout like shape to allow unobstructed grain flow when in a lowered position. However, a spring biases the door toward the raised position requiring the force exerted by the grain to maintain the door in the lowered position. As the discharging grain flow tapers off, the spring force can prematurely lift the door so as to trap an undesirable amount of grain at the discharge opening of the unloading tube. And, if a large quantity of grain remains, and the spring force is low or weak, the door can be opened by jarring and the like, so as to dribble grain.
Thus, what is sought is a grain unloading system which provides one or more of the capabilities, and overcomes one or more of the shortcomings and limitations, set forth above.